In the voice and audio encoding algorithm, because of limitations of human auditory characteristics and a bit rate, low frequency signals are usually preferentially encoded. With the development of networks, limitation for bandwidth becomes smaller and smaller, and people have higher requirements for sound quality. The sound quality of signals can be improved by increasing bandwidth of signals, and when no or a few bits exist, a bandwidth expansion technology may be adopted. As a technology of expanding a band range of voice signals and improving the quality of signals, the bandwidth expansion technology has developed remarkably in recent years and realizes commercial application in several fields, in which a bandwidth expansion algorithm in G. 729.1 and the Spectral Band Replication (SBR) technology in the Motion Picture Expert Group (MPEG) are two widely used bandwidth expansion technologies.
In the bandwidth expansion technology provided in the prior art, one method is as follows. At an encoding end, high frequency signals are not encoded, and an encoding algorithm of low frequency signals in an encoder is not changed. At a decoding end, the high frequency signals are blindly expanded according to the low frequency signals obtained by decoding and a potential relation between the high and low frequencies. In this method, as no relevant information of the high frequency signals may be referred to at the decoding end, the quality of the expanded high frequency signals is poor.
The other method is as follows. At the encoding end, information of some time envelopes and spectral envelopes of high frequency signals are encoded. At the decoding end, an excitation signal is generated according to spectral information of the low frequency signals, and the high frequency signals are recovered combining the excitation signal and the information of time envelopes and spectral envelopes of the high frequency signals obtained through decoding. Compared with the foregoing method, this method helps better the quality of the expanded high frequency signals, but for some harmonic intense signals, large distortion may easily occur; therefore, the quality of output voice and audio signals in this method also needs to be improved.